1. Field of the Invention
The present invention relates to an exhaust gas purifying system which removes harmful components contained in exhaust gas discharged from an internal combustion engine for an automobile. Particularly, the present invention relates to an exhaust gas purifying system capable of purifying hydrocarbons contained in exhaust gas in a low-temperature range before an exhaust gas purifying catalyst is activated.
2. Description of the Related Art
An exhaust gas purifying catalyst and an exhaust gas purifying system using zeolite have been proposed in order to reduce hydrocarbons (cold HC) which are discharged in large quantity in a low-temperature range at the time of starting up an engine, regardless of a gasoline engine or a diesel engine (see Japanese Patent Application Laid-Open No. H7-174017).
Moreover, for the purpose of catalytic activation at the time of starting up an engine, an electrically heated catalyst (EHC) and a system using an air pump have been also proposed (see Japanese Patent Application Laid-Open Nos. H9-256840 and H9-228828).